Process for c6-c24 alkenes by pretreatment of phosphate catalysts



United States Patent 3,433,852 PROCESS FOR C -C ALKENES BY PRETREAT- MENT OF PHOSPHATE CATALYSTS Kestutis A. Keblys, Southfield, Mich., assignor to Ethyl Corporation, New York, N.Y., a corporation of Virginia No Drawing. Filed Nov. 7, 1966, Ser. No. 592,348 US. Cl. 260-6833 7 Claims Int. Cl. C07c 5/18 ABSTRACT OF THE DISCLOSURE In dehydrogenation of dodecane to C alkenes over a heterogeneous catalyst, poor selectivity (unwanted aromatization) occurs during the initial time on stream. Operation at higher temperatures (525-600 C.) during such initial period (0.5-6.0 hours) for each of several fresh calcium nickel phosphate and calcium cupric phosphate catalysts gave better selectivity during the subsequent period at lower temperatures (400 5'0'1 C.) compared to the unfavorable product distribution during an initial period at such lower temperatures. Any of a variety of hydrocarbon feeds may be used for the line-out period.

This invention relates to a process for the preparation of olefins. More particularly this invention relates to a process for catalytically dehydrogenating paraffins having 6 or more carbon atoms to the corresponding monoolefin.

The catalytic dehydrogenation of paraffins is well known in the art. When the paraffin being dehyd'rogenated has less than six carbon atoms, the primary products are the corresponding olefin and cracking products. However, when n-parafiins having 16 or more carbon atoms are catalytically dehydrogenated by prior art processes, the product contains a substantial quantity of aromatics as well as the olefins and cracking products. Since the primary product desired is the olefin, it is desirable to improve the yield of the olefin when C and higher parafiins are dehydrogenated. The present process provides a method for improving the olefin yield in such a case. The improved olefin yield is accompanied generally by a reduction in aromatic by-product obtained.

It is therefore an object of this invention to provide a process for catalytically dehydrogenating n-paraflins having 6 or more carbon atoms. It is another object of this invention to improve the yield of olefin on catalytically dehydrogenating C and higher paraffins and reduce the aromatic by-products obtained. This and other objects of this invention will be made clear from the detailed description and claims which follow.

An embodiment of this invention is a process for preparing olefins by dehydrogenating n-paraflins having from 6 to about 24 carbon atoms, said process comprising contacting (1) a feed containing at least one of said paraflins with a catalyst consisting substantially of (a) 50 to 95 percent calcium phosphate,

(b) 5 to 50 percent of a phosphate selected from the group of nickel phosphate and cupric phosphate, and

(c) -0 to 2 percent chromia,

said catalyst having been pretreated by contacting with a fluid hydrocarbon at a liquid hourly space velocity of 0.5 to about 6, at a temperature of from 525 C. to about 560 C. and for from about 30 minutes to about 6 hours. said dehydrogenation process being carried out (2) at a temperature of from 400 C. to about 500 C.,

(3) at a pressure of from 0.5 to about 50 atmospheres,

and

(4) at a liquid hourly space velocity of 0.2 to about 10.

A preferred embodiment of this invention is the process described above wherein the n-paraifin has from about 10 to about 18 carbon atoms.

A more preferred embodiment of this invention is the process described above wherein component (b) of said catalyst is nickel phosphate.

Another more preferred embodiment of this invention, is the process described above wherein component (b) of said catalyst is cupric phosphate.

Still more preferred embodiments of this invention are the process as described above wherein the catalyst has one of the following compositions: 8.6 percent calcium phosphate, 12 percent nickel phosphate, 2 percent chromia; 86 percent calcium phosphate and 14 percent cupric phosphate.

A most preferred embodiment of this is the process described above wherein the catalyst consists of substantially 86 percent calcium phosphate and 14 percent nickel phosphate.

The parafiins which are useful in practicing this invention are hydrocarbons having 6 or more carbon atoms. Examples of these are hexane, 2-ethyl hexane, Z-methyln-nona-decane and the like. Straight chain paraflins, that is those having no branching are preferred. These are the n-parafiins. Examples of useful n-parafiins are n-hexane, n-octane, n-decane, n-eicosane, n-pentadecane and the like. The n-paraffins which are more preferred are those having from about 10 to about 20 carbon atoms. More preferred paraflins are n-dodecane, n-tetradecane, n-heptadecane, n-octadecane and the like. Mixtures of these paraffins are also useful in the practice of this invention. Thus, mixed streams containing the paraflins enumerated above can be used. Mixed streams containing paraflins having less than 6 carbon atoms may also be dehydro genated according to the process of this invention. In other words, mixed streams containing ethane, isobutane and the like and at least one of the C or higher parafiins can be utilized.

The catalyst which effects the dehydrogenation in the process of this invention is a composite comprising metal phosphates. The metal phosphate composites which are useful are (a) calcium phosphate and nickel phosphate and b) calcium phosphate and cupric phosphate. The weight ratio of the calcium phosphate to the nickel phosphate or the cupric phosphate may range from 50:50 up to 95:5. The catalyst composite may also contain up to 2 weight percent chromia. The preferred weight ratio of calcium phosphate to nickel phosphate or copper phosphate is from 20 up to 10. A most preferred catalyst is one in which the weight ratio is 86 calcium phosphate and 14 percent nickel phosphate or cupric phosphate.

The catalysts of this invention may be prepared by using any number of methods available in the art. A requirement for the preparation is that the final catalyst composite contains the phosphates described above in the weight ratios enumerated. A convenient method of preparation is the procedure of E. C. Britton, A. J. Dretzler and C. J. Noddings described in 1nd. and Eng. Chem, 43, 2871 (1951). The procedure outlined in the Britton et al. article includes two percent chromia in the calcium phosphate, nickel phosphate composite. It is to be understood, however, that the procedure can be utilized to prepare a catalyst having no chromia. Briefly, the Britton ct al. procdeure involves the precipitation of calcium phosphate and nickel phosphate from a calcium chloride-nickel chloride solution using ammonium phosphate. 'I he calcium-nickel phosphate precipitation can also be carried out using calcium nitrate and nickel nitrate solutions. When the latter salts are employed, more concentrated solutions can be used. Thus, the latter process, that is, using the nitrates rather than the chlorides, offers an advantage by allowing for the use of smaller volumes of solution. Representative preparations of the catalysts will be given in examples to follow. Although in discussing the preparation of the catalyst, reference was made to calcium phosphate-nickel phosphate, it is understood that the comments apply equally to calcium phosphate-cupric phosphate catalysts.

The temperature at which the dehydrogenation is carried out may be varied over a wide range. Thus, the process can be carried out at temperatures from 400 C. to about 500 C. A preferred temperature range is 425 C. to about 500 C.

The process may be carried out at atmospheric pres sure. The pressures above and below atmospheric may also be utilized. Generally, pressures of from 0.5 to about 50 atmospheres are used. Pressures of 0.5 to about 10 atmospheres are preferred and pressures from 0.5 to about 2.0 atmospheres are most preferred.

The process of this invention is characterized as being a continuous process. That is, the paraffin feed stream is continuously passing over or through the catalyst. Depending on the temperature and pressure used, the hydrocarbon feed may be either in a liquid or gaseous state. The rate at which this stream flows, however, is measured as a liquid hourly space velocity. Thus, the liquid hourly space velocity (LHSV) is the ratio of liquid volume of feed stream per hour to the volume of catalyst. A suitable LHSV for the present process is 0.5 to about 10. LHSV of about 0.5 to about 6 are preferred and 0.5 to about 2.0 are more preferred.

The unexpected results obtained using the process of this invention are that in addition to producing monoolefins in relatively good yields, only small amounts of aromatic products are obtained. In other words, the overall yield of olefin is increased at the expense of the aromatic products.

In practicing this invention, inert gaseous diluents such as nitrogen, carbon dioxide or steam may be advantageously employed. The ratio in moles of diluents to paraifin feed is generally in the range of 1:1 to :1.

The following examples are provided to illustrate methods of preparing the catalyst and the dehydrogenation process of this invention. All parts and percentages are by weight unless otherwise stated. All results were obtained by gas chromatographic analysis.

Example 1 In a suitable vessel 194 parts of 2.5 N-ammonium hydroxide was added to 2000 parts of 0.075 molar phosphoric acid. In a second vessel, 21.7 parts calcium chloride and 5.4 parts of nickel chloride hexahydrate were dissolved in 800 parts of water. The calcium chloridenickel chloride solution was then added to the ammonium phosphate solution with stirring. The final pH of the solution was 8.0. The solution was stirred for 30 minutes. Stirring was then discontinued and the solution was allowed to settle overnight. The liquid was then decanted from the settled precipitate. The precipitate was then resuspended in 3,000 parts of water and filtered. This washing procedure was repeated six times. After the final filtration, the precipitate cake was dried at 60 C. for 15 hours and then at 130 C. for 24 hours. The yield of calcium nickel phosphate composite was 83.4 parts.

The dried powder was then ground to pass a No. 40 mesh screen. This screened powder was then mechanically blended to contain 2 percent powdered graphite and 2 percent powdered chromia. The powder blend was then pelletized. The pellets /s long by Ms" diameter) were used in the dehydrogenation process.

The graphite serves as a lubricant in the pelletizing operation.

The catalyst composite analyzed 31 percent calcium, 5 percent nickel, 56 percent phosphate and 2 percent chromia. Using the same basic procedure, a catalyst composite containing 84 percent calcium phosphate and 16 percent nickel phosphate was also prepared.

This is the procedure of Britton et al. referred to above.

Example 2 In a suitable vessel approximately 141 parts of 14.8 M ammonium hydroxide was added to approximately 2,000 parts of 0.3 M phosphoric acid. To the resulting ammonium phosphate solution was then added slowly with stirring a solution of 208 parts of calcium nitrate tetrahydrate and 24.2 parts of cupric nitrate trihydrate. The final pH was 8.0. The solution was stirred for thirty minutes after the addition was complete. After standing overnight, the precipitate which separated was filtered and washed twice by dispersing the residue in two liters of Water. The solid precipitate was then dried for 14 hours at 60 C. and for 24 hours at C. Yield was 104 parts of powdered catalyst, which analyzed 86 percent Ca (PO and 14 percent Cu (PO The powder was ground to pass a 40 mesh screen. Two percent graphite was added to this powder and the powder was pelletized.

Examples 1 and 2 illustrate convenient methods of preparing the catalysts of this invention. As pointed out above, other suitable procedures may be used.

Example 3 A catalyst bed was prepared using the calcium phosphate-nickel phosphate-chromia catalyst of Example 1. The catalyst bed was then heated to 501 C. An n-dodecane feed was passed through the heated bed at LHSV of 1.0. The product was 40 percent C olefins, 40 percent aromatics and 20 percent cracking products at a 22.5 percent conversion.

Example 4 A catalyst bed was prepared using the calcium phosphate-nickel phosphate-chromia catalyst of Example 1. This bed was then heated to 540 C. and contacted with n-dodecane feed for three hours at a LHSV of 1.0. The LHSV was increased to 4.0 for about 4 minutes.

The bed temperature was then lowered to 500 C. The n-dodecane feed was passed through the bed at a LHSV of 1.0. The product stream was analyzed at this point. It contained 47 percent C olefins, 12 percent aromatics and 31 percent cracking products at a conversion of 16.9 percent.

The pressure under which Examples 3 and 4 were carried out was substantially atmospheric.

Examples 3 and 4 demonstrate the striking improvement in olefin yield and decrease in aromatics which pretreatment of the catalyst efiFects.

The following examples further illustrate how the process of this invention is carried out. Parts and percentages are by weight unless otherwise indicated. The pressure is substantially atmospheric except where otherwise specified.

Example 5 A catalyst bed was prepared using the calcium phosphate/nickel phosphate/chromia catalyst of Example 1. The bed was heated to 540 C. and was contacted with dodecane at a LHSV of 1.0 for three hours. The LHSV was increased to 4.0 for about three minutes.

The catalyst bed was then cooled to 450 C. Dodecane was passed through the catalyst at LHSV of 0.4. The product at this point was 77 percent C olefins, 6 percent aromatics and 17 percent cracking products at a conversion of 9.8 percent.

Example 6 The catalyst bed temperature in Example 5 was raised from 450 C. to 475 C. and dodecane was passed through the bed at a LHSV of 0.6. The product at this point was 68 percent C olefin, 8 percent aromatics, and 24 percent cracking products at a conversion of 12.8 percent.

Example 7 A catalyst bed was prepared using 86 percent calcium phosphate, 14 percent nickel phosphate catalyst prepared as in Example 1. The catalyst bed was heated to 540 C. and dodecane was passed through the bed at an LHSV of 1.0 for three hours. The dodecane LHSV was increased to 4.0 for about 4 minutes. The catalyst tem' perature was then lowered to 500 C. Dodecane was passed through the catalyst at a LHSV of 3.0. The prod not at this point was 74 percent C olefins, percent aromatics and 26 percent cracking products at a conver' sion of 12.7 percent.

Analogous results are obtained when the dodecane is replaced by any of the following hydrocarbons: hexane; n-eicosane; n-nonane; n-heptadecane; n-tetracosane; a mixture of n-dodecane and n-tetradecane; a mixture 01 n-octane, n-pentadecane and eicosane.

Example 9 A catalyst bed was prepared using an 86 percent calcium phosphate, 14 percent nickel phosphate catalyst prepared as per the Example 2 procedure. The catalyst was then heated to 540 C. and feed of n-dodecane was passed through the catalyst bed at an LHSV of 1.0 for 3 hours. The LHSV was increased to 4.0 for about 4 minutes.

The catalyst temperature was lowered to 500 C. and n-dodecane was passed through the bed at a LHSV of 2.0. The product at this point was 71 percent C olefins, 29 percent cracking products and 0 percent aromatics Similar results are obtained when the n-dodecane feed which contacts the catalyst at 540 C. is substituted with one of the following hydrocarbon compositions: 50 percent dodecane, 50 percent benzene; 10 percent ethylene, 30 percent n-butane, 10 percent toluene and 30 percent cyclohexane; 10 percent octadecene, 20 percent isobutane, 30 percent n-butane, 10 percent toluene and 30 percent eicosane; 50 percent tetracosane, 30 percent nonadecane, 10 percent tetracosene, 20 percent hexylbenzene; 100 percent paraflin wax; 40 percent benzene, 25 percent toluene, 35 percent xylene; 3 percent octene, 8 percent C -C parafiins, 25 percent methyl benzenes, 5 percent ethyl benzene, and 59 percent octane.

Example 10 A catalyst bed was prepared using the catalyst of Example 2. The bed was heated to 540 C. and n-dodecane was passed through the bed at LHSV of 1.0 for 3 hours. The LHSV was then increased to 4.0 for 4 minutes.

The catalyst temperature was then lowered to 500 C. and dodecane was passed through the bed at LHSV of 2.0. The product at this point was 60 percent C olefins, 20 percent aromatics and 20 percent cracking products at 15.1 percent conversion.

Similar results are obtained when catalyst compositions are 95 percent calcium phosphateS percent cupric phosphate; 55 percent calcium phosphate-'45 percent cupric phosphate; 72 percent calcium phosphate28 percent cupric phosphate; 90 percent calcium phosphate- 10 percent nickel phosphate; 70 percent calcium phosphate-30 percent nickel phosphate; 50 percent calcium phosphate-5 0 percent nickel phosphate and 95 percent calcium phosphate-5 percent nickel phosphate.

Example 11 -A catalyst bed is prepared using a 90 percent calcium phosphate/ 10 percent nickel phosphate catalyst. The bed is heated to 600 C. and a feed containing percent decane, 10 percent decene, 3 percent mixed C -C benzenes and 2 percent C and lower paratfins, is passed through the bed at a LHSV of 6.0 for 0.5 hours.

The catalyst temperature is then lowered to about 440 C. and n-octadecane feed is passed through the bed at a LHSV of 10.0 under a pressure of 0.5 atmosphere. The products obtained at this point are analogous to those obtained in Examples 4 through '10.

Example 12 A catalyst bed is prepared using 75 percent calcium phosphate and 25 percent nickel phosphate catalyst. The bed is heated to 565 C. and is contacted with 1-0 percent benzene, percent hexane feed for 6.0 hours at an LHSV of 0.5.

The bed is then cooled to 400 C. and a mixed tetradecane-hexadecane-octadecane stream is passed through the bed at an LHSV of 0.2 under a pressure of 50 atmospheres. The products obtained at this point are analogous to those obtained in Examples 4 through 10.

Similar results are obtained when the fresh catalyst bed in Example 12 is heated to 525 C. instead of 565 C. and is contacted with 10 percent benzene, 90 percent hexane feed for six hours at a LHSV of 0.5.

The type of fluid hydrocarbon used to pretreat the catalyst at from 525 C. to about 600 C. is not critical. The fluid hydrocarbon can be suitably selected from parafiins, parafiin wax, olefins, aromatics, alkylated aromatics and mixtures thereof. Examples of hydrocarbons which are useful for this pretreatment are C to C n-parafiins, their isomers and mixtures thereof; kerosenes; C to C cyclic saturated and olefinic hydrocarbons; C to C paraflins containing up to 10 percent olefins and up to 50 percent aromatics; alkylated aromatics having 7 to 20 carbon atoms; paraflin wax and the like. It is possible then to use a waste or commercially unattractive hydrocarbon stream to pretreat the catalyst.

Thus, any of the fluid hydrocarbons described above can be used effectively in pretreating the catalysts in the examples presented above.

The products produced by the process of this invention are mixtures of monoolefin isomers having the same number of carbon atoms as the paraffin starting material. Thus, when n-octadecane is used as a paraflin feed, the olefin portion of the product obtained is a mixture of octadecane isomers.

=The olefins produced by the process of this invention are well known compounds and have the many utilities which are known for them. For example, they are valuable chemical intermediates and can be transformed into acids by an ozonolysis reaction. Thus, for example, tetradecene-Z can be reacted with ozone to yield lauric acid, a detergent range acid. Similarly, the other olefins produced by this process can be ozonized to yield the corresponding acids. When ozonizing the products of the process of this invention, the reaction is generally carried out at a low temperature; e.g., from 50 to about 10 C. After the ozonization reaction is completed, the resultant reaction mixture is usually treated with another oxidant such as air or oxygen to obtain the product acid. ;T he secondary oxidation is usually carried out at a temperature within the range of 20 to 90 C. Solvents which can be employed in the ozonolysis of olefins include inert solvents such as chloroform and carbon tetrachloride or hydroxylic solvents such as methanol and acetic acid.

The present invention is described above. substantiating data is also presented. Claims to this invention follow. It is intended that this invention be limited only within the spirit and lawful scope of these claims.

I claim:

1. A dehydrogenation process for preparing olefins from n-parafiins having from 6 to about 24 carbon atoms, said process comprising contacting (1) a feed containing at least one of said paraffins with a catalyst consisting substantially of (a) 50 to 95 percent calcium phosphate,

(b) 5 to 50 percent of a phosphate selected from the group consisting of nickel phosphate and cupric phosphate, and

(c) 0 to 2 percent chromia,

said catalyst having been pretreated by contacting it with a fluid hydrocarbon at a liquid hourly space velocity of 0.5 to about 6 at a temperature of from 525 C. to about 560 C. and for from about 30 minutes to about 6 hours, said dehydrogenation proces being carried out (2) at a temperature of from 400 C.

500 C., (3) at a pressure of from 0.5 to about 50 atmospheres,

and (4) at a liquid hourly space velocity of 0.2 to about 10. 2. The process of claim 1 wherein the n-paraffin has from about 10 to about 18 carbon atoms.

3. The process of claim 2 wherein component (b) of said catalyst is nickel phosphate.

4. The process of claim 3 wherein the catalyst conto about sists substantially of 86 percent calcium phosphate, 12 percent nickel phosphate and 2 percent chromia.

5. The process of claim 3 wherein the catalyst consists substantially of 86 percent calcium phosphate and 14 percent nickel phosphate.

6. The process of claim 2 wherein component (b) of said catalyst is cupric phosphate.

7. The process of claim 6, wherein said catalyst consists substantially of 86 percent calcium phosphate and 14 percent cupric phosphate.

References Cited UNITED STATES PATENTS 12/1966 Haensel et a1. 260-683.3 4/1967 Abell et al. 260683.3

DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,433,852 March 18, 1969 Kestutis A. Keblys It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 42, after "10 percent ethylene," insert 30 percent hexane, 20 percent hexene and 40 percent cyclohexane; 10 percent octadecene, 20 percent isobutane,

Signed and sealed this 7th day of April 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

